On-route to dryout through sequential interfacial dynamics in annular flow boiling around temperature and heat flux controlled heater rod

Abstract

A numerical methodology is used to track the interfacial dynamics of the dryout mechanism for flow boiling around the heated cylindrical rod. The mathematical model is based on the Volume of Fluid interface capturing technique for two-phases of fluids. A single set of Navier-Stokes equations with an added source term to take care of vapor mass flux generation due to phase change is utilized. The simulations are carried out for various combinations of flow parameters and heating conditions at a representative higher working pressure of 40 bar, which is usually observed in Boiling Water Reactors (BWR). Various mechanisms of dryout, such as disturbance wave generation, droplet entrainment, deposition, rewetting, nucleation beneath the thin annular film, and its dynamics are illustrated with pictorial representations. The liquid phase fraction distribution across radial and axial planes, wall temperature, and heat transfer coefficient are used to quantify the dryout characteristics.